1. Field of Invention
The present invention relates to a mark and a method for using the same. More particularly, the present invention relates to a process monitor mark and a method for using the same.
2. Description of Related Art
Conventionally, as the numbers of the material layers formed over the substrate is increased, the surface of the topmost material layer over the peripheral region of the substrate is relatively smoother. However, in the process for patterning the topmost material layer, it is not easy to control the exposure process of the lithography process performed on the photoresist layer used for patterning the topmost material layer to have the margin of the pattern topmost material layer at a desirable position around the boundary between the peripheral region and the device region. Typically, after the topmost material layer is etched by using the patterned photoresist layer as a mask, the margin of the patterned topmost material layer is inspected (After Etching Inspection, AEI) and determined whether the margin of the patterned topmost material shifts. By referring the inspection result, in the next process run, the users adjust the exposure factors of the lithography process performed on the photoresist layer or re-align the mask while the margin of the patterned topmost material layer shifts away.
FIG. 1 is a cross-sectional view schematically illustrating a patterned topmost material layer after etching process according to the conventional process. As shown in FIG. 1A, when the pattern photoresist (not shown) shifts towards to the peripheral region 100b of the substrate 100, the margin of the patterned topmost material layer 106 is in the peripheral region 100b and is far away from the boundary between the peripheral region 100b and the device region 100a. Therefore, a large amount of the underlayer structure 104 is covered by the patterned topmost material layer 106 in the peripheral region 100b after the etching process is performed, wherein the underlayer structure 104 comprises an upper layer 104b and a lower layer 104a. Because the underlayer structure 104 in the peripheral region 100b is overly covered by the patterned topmost material layer 106, the quality of the later performed process for lifting the patterned topmost material layer 106 through the removal of upper layer 104b is poor. That is, the large amount of the topmost material layer 106 in the peripheral region 100b forbids the removal process of the upper layer 104b so that most of the topmost material layer 106 and the upper layer 104b still remain over the substrate 100 in the peripheral region 100b even after the lifting process is performed (as shown in FIG. 1B). Under the situation mentioned above, the product is regarded as failure.
FIG. 2 is a cross-sectional view schematically illustrating a patterned topmost material layer after etching process according to the conventional process. As shown in FIG. 2, when the pattern photoresist (not shown) draws back to the device region 200a of the substrate 200, the margin of the patterned topmost material layer 206 is in the peripheral region 200b and is very close to the device region 200a or even right inside the device region 200a. Therefore, the isolation structure 201 in the substrate 200 at the boundary between the peripheral region 200b and the device region 200a is easily damaged during the topmost material layer 206 is patterned. Hence, the pinhole 210 is formed in the isolation structure 201. Under the situation mentioned above, the product can no longer be used and is regarded as failure.
Since there is no way to pre-inspect the margin of the topmost material layer before it is etched, the patterned topmost material layer should be removed and reworked when the margin of the patterned topmost material layer is not at the desirable position around the boundary of the device region and the peripheral region. Therefore, the cost is increased due to the rework. Furthermore, the whole device is failure since the isolation structure is damaged during the etching process is performed on the topmost material layer.